This section is intended to provide a background to the various embodiments of the technology described in this disclosure. The description in this section may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and/or claims of this disclosure and is not admitted to be prior art by the mere inclusion in this section.
With the advancement of digital signal processing technology and the improvement in performance of wideband radio frequency devices, dual band radio receiver has become available in today's wireless communications systems.
By way of illustration, if a base station (BS) is equipped with a dual band radio receiver, it can receive from two user equipments (UEs) simultaneously in two respective frequency bands, as shown in FIG. 1.
Typically, a dual band radio receiver may be structured as shown in FIG. 2, in order to facilitate reusing part of the receiver for processing both frequency components and hence reduce the size and cost of the receiver. As illustrated, after a dual band radio signal which consists of a first frequency band component (denoted as band 1) and a second frequency band component (denoted as band 2) is received at the antenna of the receiver, it is filtered and passes through a low noise amplifier (LNA). Then, the dual band signal is filtered by two respective radio frequency (RF) filters, each of which allows a respective one of the first and the second frequency band components to pass through. Thus, the first and the second frequency band components can be attenuated independently from each other by respective attenuators. Next, by means of frequency mixing, the two frequency band components are combined into the same intermediate frequency (IF) signal, which enters a common IF stage that comprises an IF filter and an anti-aliasing (AA) filter and possibly an attenuator therebetween. Thereafter, the output from the AA filter is converted from an analog signal into a digital signal which is subject to digital processing.
In order for the dual band radio receiver to cope with the worst case where the first frequency band component has a high power (e.g., −35 dBm) while the second frequency band component has a low power (e.g., −105 dBm), automatic gain control (AGC) function must be triggered separately for the first and the second frequency band components by measuring powers of the first and the second frequency band components and determining whether the powers of the first and the second frequency band components exceed a first AGC threshold and a second AGC threshold respectively (the first AGC threshold may or may not be equal to the second AGC threshold). Supposing both the first and the second AGC thresholds are set to −45 dBm, the AGC function would be triggered only for the first frequency band component, because the power of the first frequency band component exceeds the first AGC threshold while the power the second frequency band component does not exceed the second AGC threshold. Accordingly, a lower gain would be determined and applied only for the first frequency band component, causing a noise floor increment that does not affect the identification of the first frequency band component which has a high power level. Meanwhile, the AGC function would not be triggered for the second frequency band component, no noise floor increment would be incurred, and the identification of the second frequency band component which has a low power level would not be affected.
Otherwise, if the AGC function is triggered for both the first and the second frequency band components as long as the highest one of the powers of the first and the second frequency band components (in this example, the power of the first frequency band component) exceeds a single AGC threshold, it would be impossible to identify the power of the second frequency band component because the increased noise floor due to the triggering of the AGC function would be higher than the power of the second frequency band component, as illustrated in FIG. 3.
In the prior art, two structures have been proposed for the dual band radio receiver. As illustrated in FIG. 4, one of the prior art receiver structures is characterized by inserting a coupler in each of the respective RF branches for the first and the second frequency band components and using a first power meter, a second power meter and a third digital power meter to measure the power of the first frequency band component, the power of the second frequency band component and the total power of the first and the second frequency band components respectively. Due to the use of couplers which are analog devices, the receiver structure illustrated in FIG. 4 has the advantage of being able to react fast enough to keep pace with a rapid change of the power of the received dual band radio signal (for example, due to fast quality degradation of the wireless channel on which the dual band radio signal is received). However, it suffers from drawbacks (such as large size, high power consumption and high cost) that are intrinsic to analog devices.
Instead of using couplers and directly measuring the powers of the first and the second frequency band components, the other one of prior art receiver structures as illustrated in FIG. 5 is characterized by using numerically controlled oscillators (NCOs) and baseband filters and by measuring the powers of the first and the second frequency band components after they have undergone digital processing. Because it does not include couplers, this receiver structure can be smaller in size, less power-consuming and less costly. However, it is incompetent to track a rapid change of the power of the received dual band radio signal, since its response speed is limited by the digital processing which is time-consuming.